A cornea is a transparent film in front of an eyeball that covers the iris, pupil, and anterior chamber. The cornea provides most of refractive power to the eye. A cornea with high transparency and appropriate refractive power can allow a clear image. The refractive power of the cornea mainly depends on the corneal curvature. A deformation of the cornea can lead to a change in corneal curvature. A small corneal curvature can lead to high refractive power and shortsightedness. If the deformation of the cornea can be monitored instantaneously, the change of the corneal curvature can be predicted in advance, thus allowing immediate measures to be taken to prevent the user from shortsightedness or myopia.